Cooling system for a fuel cell battery

ABSTRACT

A cooling system for a battery of fuel cells that contains at least two fuel cells, each of which comprises a membrane-electrode unit and two collector plates is disclosed. Cooling cards supplied with coolant and that are connected to one another via lines are thereby arranged between the individual fuel cell units.

FIELD OF THE INVENTION

The invention is directed to a novel cooling system for a battery offuel cells that contains at least two fuel cells, each of whichcomprises a membrane-electrode unit and two collector plates.

BACKGROUND OF THE INVENTION

Up to now, fuel cell batteries with cooling systems are known whereincoolants flow in bipolar plates that are located between the individualfuel cell units of a battery. In addition, newer cooling systems havebeen disclosed for these batteries that are cooled without bipolarplates or filter press technology in a gas or in a fluid bath (see, e.g.German Letters Patent 44 42 285) and comprise fuel cell units that canbe individually handled within the battery.

Sealing problems particularly arise in the battery cooling with bipolarplates because regions lie next to one another in which oxidant andfuel, which must be dependably sealed off from one another, areconducted. Given the fuel cell batteries without bipolar plates, whichhave only been known for a short time (see, e.g. German Letters Patent44 42 285), fundamentally only two cooling systems have hitherto beenknown that both have the coolant flow through the battery in a freestream.

Under certain circumstances, however, the problem of uniformdistribution and flow-through of the coolant within the fuel cellbattery arises in the concept of fluid cooling because the areas closeto inlet and discharge openings of the battery have a more intense flowand are thus more intensively cooled than the other areas of thebattery. It can also be disadvantageous that many component parts of thebattery enter into communication with the coolant—especially whencoolants that are incompatible with the materials of the fuel cells areemployed.

The full content of the patent bearing serial number German LettersPatent 44 42 285 is herewith referenced and the entire disclosurethereof is incorporated by reference into the subject matter of thepresent specification.

There is a need for economical batteries of fuel cells, i.e. batteriesconstructed without bipolar plates, wherein the cooling system assuresan optimally uniform distribution of the coolant within the battery.There is also a need in fuel cell batteries with bipolar plates for acooling capacity that can be added in when the battery must temporarilyyield greater powers.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to make a coolingsystem for a fuel cell battery, particularly a PEM fuel cell battery,available that assures an optimally uniform flow-through of a fuel cellbattery with coolant and/or that can be added in as needed to anexisting cooling.

The subject matter of the present invention is therefore a battery and amethod for the manufacture of a battery composed of at least two fuelcells each of which comprises a membrane-electrode unit and twocollector plates, whereby a cooling card that has thermal contact to atleast one of the neighboring fuel cells is located between the fuelcells.

In one embodiment of the invention, the individual cooling cards of abattery are connected by conduits in which coolant is conveyed.Electrically, however, the cooling cards are insulated from one another.It is cost-beneficial when the cooling cards of a battery (or of aplurality of batteries) are connected to one another but when they arealso connected to an external heat exchanger that serves forregeneration of the coolant and that, for example, can also be fashionedin the form of a heat engine.

In one embodiment, the cooling card is filled such with endothermicallyreacting medium that exhaust gases of the endothermic reaction canescape via the sealing frame element (for example, alcohol), and enoughcooling capacity is contained in a cooling card for the operatingduration of the battery that no supply or disposal line of the coolingcard are required.

In a practical development of the invention, the cooling cardsthemselves can be simply and cost-beneficially manufactured because theycan be assembled by simple scaling and/or clamping and/or plugging oftwo coined plates.

In another advantageous development, the cooling cards are joined to therespectively adjacent collector plates of the adjoining fuel cells byand adhesive that is thermally and/or electrically conductive. In yetanother embodiment, the cooling cards can be inserted as needed into thebipolar plates. Finally, the cooling cards of another embodiment of theinvention can be respectively integrated in an intermediate element thatis located between the collector plates of the individual fuel cells.Any element that serves for

transmission of the mechanical pressure between the individual fuelcells,

transmission of the electrical current between the individual fuelcells, and

elimination of the dissipated heat from the collector plate within afuel cell battery is suited as intermediate element. For example, theintermediate element disclosed in the patent application bearing theGerman serial number 196 359 0.5 (of the same assignee) is especiallywell-suited.

What is understood here by “battery” is a unit or stack of at least twoseries-connected fuel cells. Dependent on the application of the fuelcell battery (stationary fields of employment of the PEM batteries are,for example, the applications in household energy supply and indecentralized power generating; electro-traction is a mobileapplication), practice will be a matter of units having a far greaternumber of individual, series-connected fuel cells.

Fuel cells that were disclosed by German Letters Patent 44 42 285already cited above are preferably referred to here as “individual fuelcell” or “fuel cell unit”. Said fuel cells are not limited to the PEMfuel cells (see column 3, lines 18-27 of the German Patent) and areindividually handled units that respectively comprise a negative poleplate, a membrane-electrode unit and a positive pole plate, whereby theaforementioned component parts are connected to one another by a frameelement in a mechanically rigid, gas-tight and electronically insulatingfashion. The invention, however, is not limited to batteries of thesefuel cells but, as already mentioned, also covers batteries that aremanufactured with the filter press technology upon employment of bipolarplates.

In the present case, the term “membrane-electrode unit” is used in itssense familiar to a person skilled in the art, as explained in the book“Brennstoffzellen”, edited by Ledjeff, and published by Müller Verlag orin the patent specifications that have been cited.

What is referred to here as “collector or contact plate” is everyterminating plate of a fuel cell unit of the battery. This can therebybe a matter both of traditional “bipolar plates” or “bipolar plates”wherein two collector plates are combined to form bipolar plate as wellas individual pole plates as disclosed, for example, by German LettersPatent 44 42 285. Among other things, traditional bipolar plates aredescribed in the book “Brennstoffzellen” edited by Ledjeff.

What is understood by “cooling card” is every type of a welded orotherwise fashioned plate that forms a cavity for the coolant. Forexample, these are a matter of double plates that lie on top of oneanother and are joined to one another in sealing fashion along theedges. The cooling cards can contain openings for the acceptance anddischarge of coolant that are surrounded such with seal elements orsealing lips that, by simply stacking the cooling cards, lines throughwhich the coolant can flow are formed between them.

The cavities in the individual cooling cards of a fuel cell battery orof a plurality of batteries can be connected to one another via lines.These lines can be connected to any type of cooling circulation system,whereby the fashioning of the cooling circulation system is in turncompletely arbitrary, for example can be fashioned from heat engine tosimple beaters. The material of the plates that, together with the sealelements, form the cooling card must be electrically and thermallyconductive material and should exhibit enough elasticity so that it canalso be practically employed for the transmission of the mechanicalpressure in the battery and component tolerances are compensated. Forexample, stainless steel or spring bronze or other copper or aluminumalloys as well as plastics, for example metal-containing polymers, aresuitable. A surface treatment of the plates (for example, gold plating),which can also protect against corrosion, can ensue for reducing thecontact resistance and for better heat elimination to the coolant. Sucha surface treatment can be meaningful not only for the cooling cards butalso for other elements of an inventive battery.

What are understood by “lines” in the sense of the present inventionare, first, lines that are formed by the assembly of the discreteelements of a PEM fuel cell battery without additional line parts.However, the inventive lines can just as easily be composed andconstructed of finished line parts such as tubes or hoses that areintegrated into the battery. All conceivable lines and line arrangementsfor coolants are co-covered by the present invention.

The thickness of the individual plates can vary. It preferably amountsto between 0.001 mm and 1 mm, particularly preferably between 0.01 mmand 0.4 mm and, in particular, between 0.05 mm and 0.2 mm.

The manufacture of the cooling cards should be optimally cost-beneficialand simple, for example be sealing clamps and plugging two pre-coinedplates together upon employment of a seal element, which is preferablyelastic. For improved thermal and/or electrical conductivity of thecooling cards to the respectively adjoining collector plates, it can bemeaningful to utilize electrical and/or thermally conductive adhesives.For example, the entire active surface of the cooling card as well asthe cell surface of the adjacent collector plate are covered with suchadhesive (either on one or both sides) and are then pressed against oneanother. Of course, only individual points or lines of the surfaces canalso be connected via such adhesive layers. The manufacture of thecooling cards can also ensue by simply welding or soldering the doubleplates together. Any practical manufacture of cooling cards, whetherproduced single part or multi-part or whether by soldering, gluing,welding or in some other way is co-covered by the invention.

What is understood be “coolant” is a liquid (for example, water,alcohol, oil) or a gas (for example, an endothermically reacting gasmixture that gets the heat for a continuously occurring process from thewaste heat of the fuel cell).

The cooling cards can replace intermediate elements as disclosed, forexample, in the German Patent Application bearing serial number 196 35901.5 and that serve within the battery for the transmission of theelectrical power, mechanical pressure and for heat transmission orelimination. On the other hand, the intermediate element can also beretained in modified form, whereby the cooling card is either integratedinto the intermediate element or is joined to it by an electrically andthermally conductive adhesive or other connections that are electricallyand thermally conductive. For example, a connection of cooling cardand/or intermediate element to the collector plate by soldering orwelding is conceivable as long as it is assured that the mechanicalpressure, the current and the waste heat can be conducted via theseconnector parts.

In an embodiment, the present invention comprises a battery comprisingat least two fuel cell units, each fuel cell unit comprising amembrane-electrode unit disposed between two collector plates, thebattery further comprising at least one cooling card disposed betweentwo fuel cells and in thermal contact to one of the collector plates ofeach of said two fuel cells, the cooling card comprising a chamber foraccommodating coolant, the chamber being connected to an input line andan output line for circulating coolant through the cooling card, thefuel cells being disposed between the input and output lines.

In an embodiment, the cooling card is in electrical contact with saidtwo fuel cells.

In an embodiment, the input and output lines are connected to a heatexchanger.

In an embodiment, the cooling card comprises two opposing plates withthe chamber disposed therebetween, each plate having an outer peripheryjoined to the outer periphery of the other plate by at least one sealingclamp.

In an embodiment, the cooling card is connected to the collector platesof said two fuel cells by a thermally conductive adhesive.

In an embodiment, the cooling card is connected to the collector platesby an adhesive that is thermally and electrically conductive.

In an embodiment, the battery further comprises a bipolar plate and thecooling card is mounted in the bipolar plate.

In an embodiment, the present invention comprises a method ofmanufacturing a fuel cell battery comprising the steps of providing atleast two fuel cell units, each fuel cell unit comprising amembrane-electrode unit disposed between two collector plates, providingat least one cooling card comprising a chamber for accommodatingcoolant, the chamber being connected to an input line and an output linefor circulating coolant through the cooling card, placing the coolingcard between the two fuel cell units with the fuel cell units beingdisposed between the input and output lines, connecting the cooling cardto the two fuel cell units with an adhesive.

In an embodiment, the adhesive is thermally conductive.

In an embodiment, the adhesive is electrically conductive.

In an embodiment, the adhesive is electrically and thermally conductive.

In an embodiment, the present invention comprises a battery comprisingat least two fuel cell units, each fuel cell unit comprising amembrane-electrode unit disposed between two collector plates, thebattery further comprising at least one cooling card disposed betweentwo fuel cells and in contact to one of the collector plates of each ofsaid two fuel cells, the cooling card comprising a chamber foraccommodating coolant, the chamber being connected to an input line andan output line for circulating coolant through the cooling card, thefuel cells being disposed between the input and output lines andextending perpendicularly between the input and output lines, the fuelcells and cooling card being disposed parallel to one another and in astacked configuration.

Other objects and advantages of the present invention will becomeapparent from reading the following detailed description and appendedclaims, and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated below with reference to three Figures,wherein

FIG. 1 is an exploded perspective view of an embodiment of an inventivebattery wherein respectively two fuel cell units and two cooling cardscan be schematically recognized;

FIG. 2 is a sectional view of the two most common types of cooling cardswhereby FIG. 2a shows a cooling card joined by soldering or welding andFIG. 2b shows a cooling card joined by sealing clamps in crossection;

FIG. 3 is a perspective view of an inventive battery with six fuel cellunits, a front and a back cover plate as well as a screwed connectionwith tie rod.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the present invention or which render other details difficult toperceive may have been omitted. It should be understood, of course, thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows four individual parts that are assembled along the arrows 3for a functional battery. A first cooling card 1 can be seen at the veryfront, this comprising two through openings that are connected to thecorresponding openings of the second cooling card 2 via lines 5 and 6.The octagonal shape of the cooling card shows a preferred embodiment butthe shape and number of corners of the cooling cards are not intended tolimit the scope of the invention. On the contrary, every possible shapeof the cooling cards, i.e. a round or curved design as well, is includedin the invention. So that the cooling card experiences a uniformflow-through with coolant, the cooling cards 1 and 2 indicated here byway of example comprise transverse channels 4 that are schematicallyindicated by the longitudinal lines 4. The broken line 5 shows how thetwo cooling cards 1 and 2 are connected by lines. These lines arepreferably axial channels that are compounded like the remainingchannels of the fuel cell battery, for example the fuel and oxidantdelivery and discharge channels. The coolant is conducted in theselines. For example, the fresh coolant is conveyed to the cooling cardsin the right-hand line 5 and—after being used—is in turn carried offthrough the left-hand line 6. The first fuel cell unit 7 a is locatedbehind the cooling card 1, the four axial delivery and disposal channelsand the distribution channels along the cell surface again being visiblethereat.

When assembling the battery along the arrows 3, seal elements must alsobe inserted at the respective lines at their interface to the coolingcards or fuel cells in addition to the lines that, on the one hand,connect the fuel cell units to one another and, on the other hand,connect the cooling cards to one another. These seal elements can alsoalready be integrated in the fuel cell units or the cooling cards, aswas already proposed (see German Letters Patent 44 42 285) for the fuelcell units, so that further component parts are not necessary. Duringassembly, however, care must be exercised to see that the cooling cardshave no electrical contact with one another since the interveningcooling cards would otherwise be shorted. The seals are generally amatter of elastic seal material as traditionally used in fuel cellbatteries. The plurality of lines and axial channels that connect theindividual systems to one another are, of course, only an example, andit is definitely conceivable that the cooling cards, for example, areconnected to one another with more than two lines.

FIG. 2 is divided into two sub-sections, namely FIG. 2a and FIG. 2b. Themiddle of FIG. 2a shows an inventive cooling card 1 that is respectivelywelded at its corners 14. The upper sub-section 13 of the double plate,which forms the cooling card 1 in the present exemplary embodiment ofthe invention, and the lower sub-section 15 can be clearly seen. Asstated, the two individual plates 13 and 15 are, for example, pre-coinedplates for simple manufacture that are held together in sealing fashionat the edges 14, for example by soldering, welding or gluing. Theopenings with which the cooling cards are connected to one anothercannot be seen because the crossection shown here proceeds parallel tothese openings. The hatching indicates the coolant 7 that experiences auniform distribution within the cooling card due to the design of thecooling card, with forces a specific flow on the medium.

A collector plate 8 is located respectively at the top and bottomfollowing the cooling card, these collector plates 8 serving as housingof the fuel cell, for guiding the medium and for the support of theelectrolyte. Just like the cooling cards, the collector plates 8 areconnected to one another and must likewise be electrically conductive.The electrical line or series circuit of the collector plates dare alsonot be interrupted by the cooling cards. If the cooling cards haveelectrical contact to the neighboring fuel cells, it is obvious that,for example given the embodiment of the cooling card according to 2 bwherein the cooling card is formed by the sealing clamping of twoelements, that an electrically conductive connection of one collectorplate to the next collector plate must be assured via the cooling cardeither by contact within the card 1 a or via the scaling clamps 9. In aninventive battery, a fuel cell unit (membrane-electrode unit), which hasnot been shown here, is located between the two collector or contactplates 8 of FIGS. 2a and 2 b. The at least thermal and potentiallyelectrical and/or mechanical contact as well of the cooling card withthe adjacent collector plate of the collector plate of the neighboringfuel cell exists along the surfaces 11 at which the collector platesabut the cooling cards. These surfaces are either formed in that the twoparts, i.e. collector plate on the one hand and cooling card on theother hand, are mechanically pressed against one another (whereby, forexample, the tie rods at the end plates of the finished battery generatean adequate mechanical pressure) or they are formed by an adhesive thatis applied between these parts and at least thermally and potentiallyalso electrically conductively connects these parts. The embodiment isespecially beneficial wherein the contact is initially produced via themechanical pressure and is then reinforced with the thermally andpotentially also electrically conductive adhesive. An improvement of thethermal and electrical conductivity of these contact surfaces can alsobe achieved by employing an adhesive. For example, the manufacture, i.e.assembly, of a fuel cell battery can likewise be greatly simplified byglued connections. In an especially preferred embodiment, themanufacture of the cooling cards via sealing clamps as shown in FIG. 2bcan ensue via the same clamp system as disclosed, for example, in GermanLetters Patent 44 42 285. The employment of the same clamping wouldthereby have to be able to further reduce the manufacturing costs of afinished fuel cell battery. A lock-seam process as employed in themanufacture of preserve and beverage cans is also conceivable.

FIG. 3 shows a cell stack of an inventive battery with end plates andtie rods. As in the air cooled version (see German Letters Patent 44 42285), the individual cells are functional and leakage point allowsreaction gas to emerge only into the outer space and to the ambient air.Malfunctioning cells can thus be individually detected and replaced. Acooling card 1 respectively resides between two cells or fuel cellunits, and the individual cooling cards are connected to one another vialines 5 and 6. According to the preferred embodiment, a seal element orthe one sealing lip that surrounds the opening of the first cooling cardpresses such—due to the stacking—onto the other sealing lip or the otherseal element with tie rods that comprises the lines 5, 6. The supply ofthe individual fuel cell units 7 as well as of the individual coolingcards with one another ensues via lines that respectively have anadmission and a discharge connected to the end plates 25 a, 25 b of thebattery. The admission opening 24 through which the coolant 10 proceedsinto the line 5 that connects the individual cooling cards, as describedabove, can be seen at the end plate 25 a. The opening 26 through whichthe used coolant that is transported out of the line 6 (FIG. 1) in turnleaves the fuel cell stack or the battery and, for example, is suppliedto a regeneration in an heat exchanger or some other regeneration systemis shown only as discharge opening at the same level. Reaction gases aresupplied to and removed from the individual cells 7 via four channels,whereby the admission and discharge openings can be seen, for example,as opening 12 at the end plate 25 a. The tie rods 23 with which theentire battery is held together can likewise be seen at the end plate 25a.

The geometrical shapes cited by way of example and the schematicallyillustrated drawings in fact represent preferred embodiments of theinvention but are not intended to limit the scope of the invention inany way whatsoever. The area of employment of such fuel cell batteriesis broad and extends from electro-traction up to stationary employmentin the higher kilowatt range.

From the above description, it is apparent that the objects of thepresent invention have been achieved. While only certain embodimentshave been set forth alternative embodiments and various modificationswill be apparent from the above description to those skilled in the art.These and other alternatives are considered equivalents and within thespirit and scope of the present invention.

What is claimed is:
 1. A battery comprising: at least two fuel cellunits, each fuel cell unit comprising a membrane-electrode unit disposedbetween two collector plates and having a bipolar plate, the batteryfurther comprising at least one cooling card being mounted in thebipolar plate between two fuel cells and in thermal contact to one ofthe collector plates of each of said two fuel cells, the cooling cardcomprising a chamber for accommodating coolant, the chamber beingconnected to an input line and an output line for circulating coolantthrough the cooling card, the fuel cells being disposed between theinput and output lines.
 2. The battery of claim 1 wherein the coolingcard is in electrical contact with said two fuel cells.
 3. The batteryof claim 1 wherein the input and output lines are connected to a heatexchanger.
 4. The battery of claim 1 wherein the cooling card comprisestwo opposing plates with the chamber disposed therebetween, each platehaving an outer periphery joined to the outer periphery of the otherplate by at least one sealing clamp.
 5. The battery of claim 1 whereinthe cooling card is connected to the collector plates of said two fuelcells by a thermally conductive adhesive.
 6. The battery of claim 1wherein the cooling card is connected to the collector plates by anadhesive that is thermally and electrically conductive.
 7. A method ofmanufacturing a fuel cell battery comprising the steps of: providing atleast two fuel cell units, each fuel cell unit comprising amembrane-electrode unit disposed between two collector plates and havinga bipolar plate, providing at least one cooling card comprising achamber for accommodating coolant, the chamber being connected to aninput line and an output line for circulating coolant through thecooling card, placing the cooling card between the two fuel cell unitswith the fuel cell units being mounted in the bipolar plate and betweenthe input and output lines, connecting the cooling card to the two fuelcell units with an adhesive.
 8. The method of claim 7 wherein theadhesive is thermally conductive.
 9. The method of claim 7 wherein theadhesive is electrically conductive.
 10. The method of claim 7 whereinthe adhesive is electrically and thermally conductive.
 11. A batterycomprising: at least two fuel cell units, each fuel cell unit comprisinga membrane-electrode unit disposed between two collector plates andhaving a bipolar plate, the battery further comprising at least onecooling card being mounted in the bipolar plate between two fuel cellsand in contact to one of the collector plates of each of said two fuelcells, the cooling card comprising a chamber for accommodating coolant,the chamber being connected to an input line and an output line forcirculating coolant through the cooling card, the fuel cells beingdisposed between the input and output lines and extendingperpendicularly between the input and output lines, the fuel cells andcooling card being disposed parallel to one another and in a stackedconfiguration.
 12. The battery of claim 11 wherein the cooling card isin electrical contact with said two fuel cells.
 13. The battery of claim11 wherein the input and output lines are connected to a heat exchanger.14. The battery of claim 11 wherein the cooling card comprises twoopposing plates with the chamber disposed therebetween, each platehaving an outer periphery joined to the outer periphery of the otherplate by at least one sealing clamp.
 15. The battery of claim 11 whereinthe cooling card is connected to the collector plates of said two fuelcells by a thermally conductive adhesive.
 16. The battery of claim 11wherein the cooling card is connected to the collector plates by anadhesive that is thermally and electrically conductive.